AD53500JRPZ Analog Devices Inc, AD53500JRPZ Datasheet - Page 5

• Manufacturer Part Number: AD53500JRPZ
• Manufacturer: Analog Devices Inc

Specifications of AD53500JRPZ

• Mounting: Surface Mount
• Pin Count: 20
• Lead Free Status / RoHS Status: Compliant

APPLICATION INFORMATION
Power Supply Distribution, Bypassing and Sequencing
The AD53500 draws substantial transient currents from its
power supplies when switching between states and careful de-
sign of the power distribution and bypassing is key to obtaining
specified performance. Supplies should be distributed using
broad, low inductance traces or (preferably) planes in a multi-
layered board with a dedicated ground-plane layer. All of the
device’s power supply pins should be used to minimize the inter-
nal inductance presented by the part’s bond wires. Each supply
must be bypassed to ground with at least one 0.1 F capacitor;
chip-style capacitors are preferable as they minimize inductance.
One or more 10 F (or greater) Tantalum capacitors per board
are also advisable to provide additional local energy storage.
The AD53500’s current-limit circuitry also requires external
bypass capacitors. Figure 2 shows a simplified schematic of the
positive current-limit circuit. Excessive collector current in
output transistor Q49 creates a voltage drop across the 5
resistor, which turns on PNP transistor Q48. Q48 diverts the
rising-edge slew current, shutting down the current mirror and
removing the output stage’s base drive. The V
be bypassed to the positive supply with a 0.039 F capacitor,
while the V
the negative supply. These capacitors ensure that the AD53500
does not current-limit during normal output transitions up its
full 8 V rated step size. Both capacitors must have minimum-
length connections to the AD53500. Here again, chip capacitors
are ideal.
Several points about the current-limit circuitry should be noted.
First, the limiting currents are not tightly controlled, as they are
functions of both absolute transistor V
ture; higher dc output current is available at lower junction
temperatures. Second, it is essential to connect the V
REV. 0
LDCPL
pin (not shown) requires a similar capacitor to
BE
and junction tempera-
HDCPL
pin should
HDCPL
–5–
capacitor to the positive supply (and the V
negative supply)—failure to do so causes considerable thermal
stress in the current-limiting resistor(s) during normal supply
sequencing and may ultimately cause them to fail, rendering the
part nonfunctional. Finally, the AD53500 may appear to func-
tion normally for small output steps (less than 3 V or so) if one
or both of these caps is absent, but it may exhibit excessive rise
or fall times for steps of larger amplitude.
The AD53500 does not require special power-supply sequenc-
ing. However, good design practice dictates that digital and
analog control signals not be applied to the part before the sup-
plies are stable. Violating this guideline will not normally de-
stroy the part, but the active inputs can draw considerable
current until the main supplies are applied.
Stage and Positive Current-Limit Circuitry
Figure 2. Simplified Schematic of the AD53500 Output
CONTROL CURRENT
RISING-EDGE SLEW
LEVEL-SHIFTED
LOGIC DRIVE
V–
Q48
LDCPL
Q50
Q49
5
AD53500
capacitor to the
V
V+
V
OUT
HDCPL
H